JP2002-115739A, published by Japan Patent Office in 2002 proposes a gas spring comprising a piston enclosed in a cylinder filled with gas, and a piston rod connected to the piston, which projects from the cylinder in an axial direction via a bearing under the pressure of the gas acting on the piston.
A retainer is fixed to the inner circumference of the cylinder between the bearing and the piston so as to limit the displacement of the piston in an elongation direction. The piston rod projects outside the cylinder through the retainer and the bearing. A dust seal is fitted onto the bearing to cause the piston rod to slide on the dust seal, thereby preventing dust from infiltrating the cylinder. The open end of the cylinder is bent inward to retain the dust seal and prevent it from dropping out of the cylinder.